Light dimmer for solid state ballast

Abstract

A system for controlling the current in a solid state, high frequency ballast energizing a gaseous discharge lamp for providing light dimming therein is disclosed. The ballast includes a thyristor/capacitor inverter bridge for generating the lamp current which is regulated by a commutation circuit synchronized with zero crossings of the thyristor current. Lamp current and voltage level signals are fed back to the commutation circuit for proper lamp current regulation. A dimming signal is added to either the lamp current feedback or voltage feedback signal and this composite signal is provided to the lamp current regulator in varying the bias thereof for selectively controlling light intensity. Dimming may be accomplished either manually by means of a rotatable switch having an output which varies linearly with shaft rotation or automatically by means of an ambient light level sensor to provide a predetermined output light level which may be manually adjusted. A common isolated control line facilitates photosensing control in a multiple ballast/light system with inter-ballast and ground isolation provided by optoisolators. In a preferred embodiment, a user adjustable balanced bridge is responsive to either manual or light level-dependent automatic control inputs for varying the bias of an input amplifier of the lamp current regulator.

I claim: 
     
       1. In a high frequency solid state ballast for energizing gaseous discharge lamp means, a dimming circuit for varying the current in said gaseous discharge lamp means comprising: an inverter circuit for receiving power from a line source and generating a high frequency inverter signal, said inverter circuit coupled to said lamp means for providing said high frequency inverter signal thereto;   first detector circuit means responsive to signals in said lamp means for generating a timing signal in timed relation with said inverter signal;   reference voltage generator means for generating a reference voltage;   current sensor circuit means coupled to said lamp means and responsive to the current flowing therein and coupled to said reference voltage source for receiving and comparing said reference voltage with a signal representing the current in said lamp means and for generating an output signal in response to said comparison;   control logic means responsive to said timing signal and said output signal for actuating said inverter circuit to regulate the current in said lamp means;   a current source derived from said line source; and   first variable control means coupled to said current source and to said current sensor circuit means and said lamp means for generating a dimming control signal and combining said dimming control signal with said signal representing the current in said lamp means for providing a composite control signal to said current sensor circuit means wherein said composite control signal is compared with said reference voltage for selectively varying the output signal provided to said control logic means in actuating said inverter circuit and controlling the intensity of said gaseous discharge lamp means.   
     
     
       2. The apparatus of claim 1 wherein said current sensor circuit means includes a differential amplifier having as one input said reference voltage signal and as another input a composite signal comprised of the output of said current source and a signal representing the current in said lamp means for comparing said reference and composite signals and providing said output signal to said commutation circuit in response to said comparison. 
     
     
       3. The apparatus of claim 1 further comprising rectifier circuit means receiving power from said line source for generating a rectified current and for applying the same to said inverter circuit and said current source. 
     
     
       4. The apparatus of claim 1 further comprising second variable control means coupled to said first variable control means for selectively establishing the output signal level for gaseous discharge lamp means turn-off. 
     
     
       5. The apparatus of claim 4 wherein said first and second variable control means each include a selectively variable resistance coupled to said current source for controlling the current provided to said current sensor circuit means. 
     
     
       6. The apparatus of claim 1 further comprising manual switch means coupled to said line source and to said first variable control means for selectively varying the current in said current source and said output signal to said control logic means for manually controlling the current in and the intensity of said gaseous discharge lamp means. 
     
     
       7. The apparatus of claim 1 wherein said first variable control means includes light level detecting means for sensing ambient light level for automatically controlling the current in and the intensity of said gaseous discharge lamp means. 
     
     
       8. The apparatus of claim 7 wherein said first variable control means further includes a balanced bridge circuit having first and second branches, said first branch including said light level detecting means and said second branch including variable resistance means for selectively balancing said bridge in automatically controlling the current in and the intensity of said gaseous discharge lamp means. 
     
     
       9. In a solid state ballast for energizing gaseous discharge lamp means by means of an alternating current line source, a dimming circuit for varying the intensity of said gaseous discharge lamp means comprising: rectifier circuit means coupled to said line source for generating a direct current output signal;   an inverter circuit coupled to said rectifier circuit means for receiving said direct current output signal and for generating a high frequency inverter signal, said inverter circuit coupled to said lamp means for providing said high frequency inverter signal thereto;   first detector circuit means responsive to signals in said lamp means for generating a timing signal in timed relation with said inverter signal;   current sensor circuit means coupled to said lamp means and responsive to the current flowing therein for generating an output signal representative of the magnitude of said current;   control logic means responsive to said timing signal and said output signal for actuating said inverter circuit to regulate the current in said lamp means;   first variable control means coupling said rectifier circuit means to said current sensor circuit means for varying the output signal provided to said commutation circuit means in controlling the current in and the intensity of said gaseous discharge lamp means;   selectively variable manual switch means coupling said line source to said first variable control means for manually varying said output signal therefrom and the intensity of said gaseous discharge lamp means;   light level detecting means coupled to said first variable control means, said light level detecting means responsive to ambient light level for varying the output signal of said first variable control means in response thereto in automatically controlling the intensity of said gaseous discharge lamp means; and   second variable control means coupled to said first variable control means for selectively establishing the output signal level for gaseous discharge lamp means turn-off.   
     
     
       10. In a solid state ballast for energizing gaseous discharge lamp means, a dimming circuit for varying the current in said gaseous discharge lamp means comprising: an inverter circuit for receiving power from a line source and generating a high frequency inverter signal, said inverter circuit coupled to said lamp means for providing said high frequency inverter signal thereto;   first detector circuit means responsive to signals in said lamp means for generating a timing signal in timed relation with said inverter signal;   current sensor circuit means coupled to said lamp means and responsive to the current flowing therein for generating an output signal representative of the magnitude of said current;   control logic means responsive to said timing signal and said output signal for actuating said inverter circuit to regulate the current in said lamp means;   a selectively variable current source; and   optoisolator coupling means for coupling said variable current source to said current sensor circuit means in providing a composite signal comprised of a feedback signal from said lamp means and a control signal from said variable current source to said current sensor circuit means for selectively controlling the output signal of said current sensor circuit means to said control logic means in regulating the current in said lamp means, wherein said line source and said gaseous discharge lamp means are electrically isolated from said variable current source.   
     
     
       11. The apparatus of claim 10 wherein said optoisolator coupling means includes a light emitting diode electrically coupled to said variable current source and optically coupled to a phototransistor, said phototransistor electrically coupled to said current sensor circuit means and responsive to the control signal output from said variable current source. 
     
     
       12. In a solid state ballast for energizing gaseous discharge lamp means from an alternating line source input, said ballast including rectifier circuit means and inverter circuit means for converting said alternating line source input to a high frequency signal for driving said gaseous discharge lamp means, said ballast further including control logic means coupled to said inverter circuit means and to lamp current sensor means and responsive to the current in said gaseous discharge lamp means as provided to said lamp current sensor means for regulating drive signals provided to said inverter circuit means and the current in said gaseous discharge lamp means, a digital dimming circuit for varying the current in said gaseous discharge lamp means comprising: a control circuit coupled to said rectifier circuit means for providing a dimming control signal in response to control inputs thereto;   a pulse forming circuit coupled to said control circuit and responsive to said dimming control signal for generating a first pulsed output signal representing said dimming control signal; and   optoisolator means coupled to said pulse forming circuit for receiving said first pulsed output signal and for generating a second pulsed output signal in response thereto, said first and second pulsed output signal being electrically isolated from one another, wherein said optoisolator means is coupled to said lamp current sensor means for providing a digital dimming signal thereto.